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Abstract

The process of sensor validation through experimentation with the Omnisens Distributed Temperature and Strain (DITEST) Brillouin Optical Time Domain Analyzer (BOTDA) proved to be a challenging project. The project encompassed sensor calibrations, system error minimization, sensor network design and deployment, and the characterization of temperatures in the Orphan Boy Mine shaft. Fiber-optic cable sensor calibrations yielded linear relationship coefficients 0.6-1.0MHZ/°F, indicating a strong positive correlation between Brillouin Frequency Shifts and temperature. Calibrated sensors demonstrated accuracies near ±0.8°F using the corrected error bounds from residual analyses as the benchmark. Fiber-optic measurement accuracy and repeatability were controlled by user-selected signal interrogator settings and design limitations within the system.

Temperatures monitored during the February-July 2016 period showed little variation except when the Geothermal Heat Exchange System was in operation. A test of the geothermal system (used to heat the Natural Resources Building on the Montana Tech campus) was documented by the fiber-optic sensor cluster deployed in this project and separately by a temperature transducer from the Montana Bureau of Mines and Geology. Temperature was an auxiliary sensing function of the DITEST; temperature profiles recorded in time and depth demonstrated the capability of the Brillouin-based signal interrogator when used primarily as a temperature sensing system.